The [@@iterator]() method of Array instances implements the iterable protocol and allows arrays to be consumed by most syntaxes expecting iterables, such as the spread syntax and for...of loops. It returns an array iterator object that yields the value of each index in the array.
The initial value of this property is the same function object as the initial value of the Array.prototype.values property.
Syntax
array[Symbol.iterator]()
Parameters
None.
Return value
The same return value as Array.prototype.values: a new iterable iterator object that yields the value of each index in the array.
Examples
Iteration using for...of loop
Note that you seldom need to call this method directly. The existence of the @@iterator method makes arrays iterable, and iterating syntaxes like the for...of loop automatically call this method to obtain the iterator to loop over.
HTML
<ul id="letterResult"></ul>
JavaScript
const arr = ["a", "b", "c"];
const letterResult = document.getElementById("letterResult");
for (const letter of arr) {
const li = document.createElement("li");
li.textContent = letter;
letterResult.appendChild(li);
}
Result
Manually hand-rolling the iterator
You may still manually call the next() method of the returned iterator object to achieve maximum control over the iteration process.
const arr = ["a", "b", "c", "d", "e"];
const arrIter = arr[Symbol.iterator]();
console.log(arrIter.next().value); // a
console.log(arrIter.next().value); // b
console.log(arrIter.next().value); // c
console.log(arrIter.next().value); // d
console.log(arrIter.next().value); // e
Handling strings and string arrays with the same function
Because both strings and arrays implement the iterable protocol, a generic function can be designed to handle both inputs in the same fashion. This is better than calling Array.prototype.values directly, which requires the input to be an array, or at least an object with such a method.
function logIterable(it) {
if (typeof it[Symbol.iterator] !== "function") {
console.log(it, "is not iterable.");
return;
}
for (const letter of it) {
console.log(letter);
}
}
// Array
logIterable(["a", "b", "c"]);
// a
// b
// c
// String
logIterable("abc");
// a
// b
// c
// Number
logIterable(123);
// 123 is not iterable.